1. Industrial Field of the Invention
The present invention generally relates to a liquid crystal display device (LCD). More particularly, the present invention relates to, in LCDs comprising a pair of substrates disposed opposed to each other to constitute a liquid crystal panel, those having a distinguished future in the arrangement of a light-shield film provided to the substrate carrying thereon a thin film transistor (TFT).
2. Prior Art
Liquid crystal display devices are widely used as display devices of a projection type or of a direct-view type. In particular, a so-called active-matrix drive type LCD comprising pixels that are each driven individually by a TFT is useful to implement a high resolution color display. Excellent display characteristics can be realized by employing the active-matrix drive, because the cross talk among the pixels, which is a problem in a passive matrix display, can be eliminated.
In case of an active-matrix driven LCD, TFTs are provided to one of the pair of glass substrates constituting the liquid crystal panel, and each of the TFTs controls the voltage applied to the corresponding transparent pixel electrode. A TFT is a semiconductor element whose characteristics fluctuate when it is directly irradiated by an external light. Thus, a structure which cuts off external light must be provided to a TFT. Light-shield is particularly important for the protection of a projection type display device, because intense light is irradiated thereto.
On the other hand, the boundary portion of each of the pixels constituting the LCD is often influenced by the electric field of the neighboring pixels in such a manner to allow the light to pass through the portion. To improve the contrast ratio of the display, the light passing through the TFT forming portion should be minimized. Accordingly, there is proposed a structure called "black matrix" (sometimes referred to simply as "BM") to omit the boundary portion from the display area. The black matrix is also used for the purpose of cutting light, because the black matrix itself has a light-shield effect. The black matrix structure or any structure having a simple light-shield effect is provided in the form of a film, and is therefore called as "light-shield film".
Conventionally, a light-shield film (black matrix) has been formed on the substrate disposed opposed to the substrate carrying thereon the TFTs. In such a constitution, however, a precise alignment of the substrates is necessary so that the light-shield film may cover the corresponding TFT, and such a precise alignment consumes time in the assembly process. One might think of forming the light-shield pattern larger as to facilitate the alignment process, but this brings about another problem of losing brightness.